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 holl_ands | Home > Loop Antennas incl Folded Dipole > 
Hi-VHF Folded Dipoles
Hi-VHF Folded Dipoles with wide variance in element sizes analyzed using 4nec2.
Example 4nec2 files included for most antennas.

Here's an on-line Folded Dipole Calculator:
http://www.k7mem.150m.com/Electronic_Notebook/antennas/folded_dipole.html
Note that IF element diameters are the same, impedance does not change as you vary the separation.
By adding a Reflector and a Director, you've got a simple 3-Element YAGI:
http://www.wfu.edu/~matthews/misc/dipole.html

Some DIY Folded Dipole examples:
oldsyd's (new) Ch7: http://img4.imageshack.us/img4/6002/foldeddipole1.jpg
oldsyd's (old) Ch7: http://img23.imageshack.us/img23/180/0000241.jpg
mlord's Ch6: http://www.digitalhome.ca/forum/showthread.php?p=833571

There is a Quasi-optimum Separation between Folded Dipole Elements of about two inches for larger diameters,
one inch for moderate and 1.0 to 0.5 inch for small wires.  But a 2:1 variation causes only small differences in SWR.

Hi-VHF sizes providing best SWR and Net Gain (centered on CH9/10) are:
27.0 x 2.0 inch - One Inch Diameter Copper Tubing
27.5 x 2.0 inch - 1/2-in Copper Tubing (Type M)
28.0 x 1.5 inch - 5/16-in O.D. Copper Tubing (not much better than quarter inch)
28.0 x 1.0 inch - Quarter Inch O.D. Copper Tubing (or RG-58/59 Braid Shield Coax)
28.25 x 0.75 inch - AWG12 Copper Wire (may leave insulation on in VHF band)
24.50 x 0.5 inch - AWG24 Copper Wire (may leave insulation on)
[ALL MEASUREMENTS ARE CENTER-TO-CENTER.]

Sizes may be rescaled by same fraction as frequencies change, using LONGER elements for LOWER frequencies.
For example, minimum SWR for AWG12 occurs at 192 MHz (between Ch9&10).  To move minimum SWR to 207 MHz (Ch12),
shorten 28.25-in by fraction 192/207 or 26.2-in.  Separation between Folded Dipole Elements won't make much difference.

QtrInchCopper Tubing, 1/2-in Type M Copper Tubing and 1-in O.D. provide good SWR across entire Hi-VHF band.
AWG12 and AWG24 are best ONLY over 2 adjacent channels (Ch9-10 example shown).

Total parts cost: about $10 for 10-ft piece of 1/2-in Type M Copper Tubing, 4 Copper Elbows, 2 Caps and a cheap Balun.

FYI: johnrmckee measured 0.5 dB VHF/UHF loss for Philips Outdoor Balun:
http://www.avsforum.com/avs-vb/showthread.php?p=15851345
This is consistent to what I've measured for Radio Shack, RCA and Channel Master Baluns at VHF.
But Philips Outdoor Balun is first one I've seen with low loss across the UHF Band.

So after finishing these NEC Sim runs, I was Googling around for some additional Folded Dipole examples:
Yup, it's 1/2-in Copper Pipe with 4 Elbows:  http://pigtail.net/nicholas/ctn/dipole.html

EDIT (22Jun2009): Added photos of DIY construction for a Hi-VHF Folded Dipole using 1/2-in Copper Pipe.
Since he actually had (one and only one) experience brazing a pipe joint....and the tools...my son did this job.
Last week he had to replace a corroded valve on his water heater....making him an expert compared to me....

EDIT (28Jun2009): Hung Hi-VHF Folded Dipole (1/2-in Pipe version) at 7-ft height on Outdoor Pergola 70-miles SE fm Mt Wilson (L.A.).
Ch7/9 very watchable but weak (80-90% QUALITY on Dish vip622 DVR with 65-70% "SIGNAL STRENGTH").
Did not expect Ch11/13 due to Ch12 being only 2.7 miles away and Folded Dipole doesn't have sharp null in requisite direction.

EDIT (3Sep2011): Used 4nec2 to analyze different Feedpoint Gap sizes in a Folded Dipole (L=27.5, OD=0.569-in Cu).
Raw Gain and Net Gain were within 0.1 dB, whether 0.75, 1.0 or 1.45-in, so Gap Size in Unimportant.
BTW: 1.45-in is the Source segment size in the posted 4nec2 file with one continuous driven element.  It was not possible
to test 0.5-in Gap size, due to 4nec2 declaring errors due to it's small size, not fixable with different AutoSeg( ) choices.

EDIT (22Nov2012): Moved Ch6 and Vertical FM Charts to new Lo-VHF Folded Dipole album.
Date(s): 15 July 2009. Album by holl_ands. 1 - 41 of 41 Total. 7458 Visits.
Start SlideshowTo order prints and photo-products: 1. Select photos. 2. Click Order. 3. Select products.Select images and click to download to your computer 
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Hi-VHF Folded Dipole - Net Gain for Different Diameters

1/2-in Copper Tube with four Elbows looks good.
Total cost about $10 incl. a cheap Balun.


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Hi-VHF Folded Dipole - SWR for Different Diameters

Length adjusted for equal SWR at freq extremes.
[I wasn't as finicky with some of them...]


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Hi-VHF Folded Dipole - Outdoor on Pergola
Ch7/9 barely OK 70-miles from Mt Wilson (L.A.)

Didn't expect Ch11/13 due to Ch12 (2.7 miles)
blocking adjacent channel reception.


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Clean all connections down to bare metal.
Thin coat of Plumbers Soldering Flux (round tin).

Seal Brass screw inside Cap pieces.
Torch and Plumbers Tin/Silver Solder.


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Brazing end pieces

Only other brazing job (ever) was last
week to fix a corroded valve on the water heater.

"I would just like to point out that ..."
View Comments...

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Brazing Cap pieces.

Fluxed everything & reheat for final seal while
wiping off excess solder with wet rag.

Hi-VHF (Ch7-13) full-band coverage size is
27.5-in x 2.0-in Center-to-Center

Ch5/6/FM size is 63-in x 2-in Center-to-Center.


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Hi-VHF Folded Dipole - Raw Gain
One Inch O.D. Copper Tubing
27-inches x 2 inch


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Hi-VHF Folded Dipole - SWR
One Inch O.D. Copper Tubing
27-inches x 2 inch


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Hi-VHF Folded Dipole - Impedance
One Inch O.D. Copper Tubing
27-inches x 2 inch


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Hi-VHF Folded Dipole - Raw Gain
0.569-in O.D. Copper Tubing
27.5-inches x 2 inch


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Hi-VHF Folded Dipole - SWR
0.569-in O.D. Copper Tubing
27.5-inches x 2 inch


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Hi-VHF Folded Dipole - Impedance
0.569-in O.D. Copper Tubing
27.5-inches x 2 inch


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Hi-VHF Folded Dipole - Raw Gain
5/16-in O.D. Copper Tubing
28.0-inches x 1 inch


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Hi-VHF Folded Dipole - SWR
5/16-in O.D. Copper Tubing
28.0-inches x 1 inch


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Hi-VHF Folded Dipole - Impedance
5/16-in O.D. Copper Tubing
28.0-inches x 1 inch


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Hi-VHF Folded Dipole - Raw Gain
5/16-in O.D. Copper Tubing
Ch2-13 Raw Gain


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Hi-VHF Folded Dipole - Raw Gain
5/16-in O.D. Copper Tubing
Ch2-13 SWR (300-ohms)


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Hi-VHF Folded Dipole - Raw Gain
5/16-in O.D. Copper Tubing
Ch2-13 Impedance


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Hi-VHF Folded Dipole - Raw Gain
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole - SWR
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole - Impedance
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole: 3D Total Gain Pattern at 198 MHz
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole: 3D Horiz. Gain Pattern at 198 MHz
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole: 3D Vert. Gain Pattern at 198 MHz
Quarter Inch Copper Tubing
28-inches x 1 inch


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Hi-VHF Folded Dipole - Raw Gain
AWG12 Copper Wire
28.25-inches x 1 inch


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Hi-VHF Folded Dipole - SWR
AWG12 Copper Wire
28.25-inches x 1 inch


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Hi-VHF Folded Dipole - Impedance
AWG12 Copper Wire
28.25-inches x 1 inch


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Hi-VHF Folded Dipole - Raw Gain
AWG24 Copper Wire
28.5-inches x 1 inch


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Hi-VHF Folded Dipole - SWR
AWG24 Copper Wire
28.5-inches x 1 inch


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Hi-VHF Folded Dipole - Impedance
AWG24 Copper Wire
28.5-inches x 1 inch


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Hi-VHF Folded Dipole
AWG24 Copper Wire
Hi-VHF Raw Gain


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Hi-VHF Folded Dipole
AWG24 Copper Wiring
Hi-VHF SWR (300-ohms)


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Hi-VHF Folded Dipole
AWG24 Copper Wire
Hi-VHF Impedance


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Hi-VHF Folded Dipole
AWG24 Copper Wiring
Ch2-13 Raw Gain


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Hi-VHF Folded Dipole
AWG24 Copper Wiring
Ch2-13 SWR (300-ohms)


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Hi-VHF Folded Dipole
AWG24 Copper Wiring
Ch2-13 Impedance


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Hi-VHF Folded Dipole: L=27.5, OD=0.569-in
Feedpoint Gap Size is Unimportant
NOTE: Negligible 0.005 dB differences.

"Thanks Holl_ands! Good to know feed..."
View Comments...

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Average Gain Test = 1.0 is typical for all runs.
Verifies accuracy of NEC Sim results.


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DOC39
Hi-VHF Folded Dipole - Example 4nec2 file
Modify parameters for different sizes.


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4nec2 Parameter Sweep for Gap Size
Total Gain on 198 MHz
This is utter NONSENSE!!!!!


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4nec2 Parameter Sweep for Gap Size
Horizontal Gain on 198 MHz
This is utter NONSENSE!!!!!


 
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  Sign the Guestbook. Displaying 2 of 2 entries.
Great site! I can clear up your ideas about gap size. In practice the feed wire (any type) takes up the gap so there is NO practical difference no matter how wide it is.
 - 
Keith, Mon, 19 May 2014 7:51PM
I can use this website alot. I like to build my own antennas. Thank You very much.
 - 
Doug McAbee | none, Mon, 31 Oct 2011 5:50PM